When referring to the transmission of TM modes and/or TM waves, only the electric field has components in the direction of propagation and the magnetic fields are situated only in the plane perpendicular to the direction of propagation. TM waves are therefore also referred to as E waves.
U.S. Pat. No. 6,549,092 B1 discloses a high-frequency filter comprising a plurality of resonator chambers interconnected through openings. Each resonator chamber contains a dielectric material and an internal conductor, wherein the internal conductor is designed in one piece with the housing. The internal conductor is energized by means of a feeder line by means of which the dielectric material is also energized. The complex design is a disadvantage of this high-frequency filter, which necessarily results in greater deviations in the filter properties during production.
The publication “Compact Base Station Filters Using TM Mode Dielectric Resonators” by M. Höft and T. Magath describes the structure of a high-frequency filter having a plurality of dielectric resonators. The coupling between the individual resonators is in parallel to the direction of propagation of the H field.
It is a disadvantage of this design that it requires more space to be able to implement the desired filter properties. The space required increases as more signal transmission paths are to be formed.
The example non-limiting technology herein creates a high-frequency filter, which is suitable in particular for transmission of TM modes in transverse direction. This high-frequency filter has a space-saving design, on the one hand, while being simple and inexpensive to manufacture, on the other hand.
The example technology provides a high-frequency filter and method for adjusting such a high-frequency filter.
The high-frequency filter comprises at least n resonators, each of which has a resonator chamber enclosed by the housing, where n≥2, preferably n≥3, more preferably n≥4, even more preferably n≥5. The high-frequency filter also has at least n dielectrics, at least one of which is arranged in one resonator chamber of the n resonators. The resonator channels of the n resonators are arranged against one another in the direction of signal transmission, where the direction of signal transmission runs at a right angle to or primarily at a right angle to the H field. Each resonator chamber is adjacent to at most two other resonator chambers and is isolated from each of the other resonator chambers by one of n−1 isolation devices. Each of the n−1 isolation devices has at least one coupling opening, wherein adjacent resonator chambers are coupled to one another exclusively by means of these coupling openings in the corresponding isolation device. The coupling between the resonator chambers is at a right angle or with one component predominantly at a right angle to the H field. A first signal line terminal is coupled through a first opening in the housing, in particular in the housing cover, to the at least one dielectric of the first resonator, wherein    a) the first signal line terminal is in central or eccentric contact with the dielectric in the resonator chamber of the first resonator;            or            b) the dielectric has a recess in the resonator chamber of the first resonator into which the first signal line terminal protrudes;            or            c) the dielectric in the resonator chamber of the first resonator has a continuous recess through which the first signal line terminal comes in contact with the first isolation device.
Additionally or alternatively, this is also true of the second signal line terminal, which protrudes into the nth resonator chamber. This one is coupled to the dielectric of the nth resonator through a second opening in the housing, in particular in the housing bottom, wherein    a) the second signal line terminal is in central or eccentric contact with the dielectric in the resonator chamber of the nth resonator;            or            b) the dielectric in the resonator chamber of the nth resonator has a recess into which the second signal line terminal protrudes;            or            c) the dielectric in the resonator chamber of the nth resonator has a continuous recess through which the second signal line terminal extends, so that the second signal line terminal is in contact with the n−1th isolation device.
Due to the fact that the coupling takes place at a right angle to the H field in particular, the resonator may also have a compact design. In addition, very good filter results are achieved because the dielectric which is directly in contact with the signal line terminal is energized directly by it. This energization does not take place indirectly due to the fact that the TM wave first propagates in the cavity of the resonator and optionally also energizes an internal conductor, by means of which the dielectric is then energized to oscillation.
The first signal line terminal and/or the second signal line terminal is/are preferably in contact with the first and/or nth dielectric and/or with the first and/or n−1th isolation device, being arranged perpendicular to the surface of the isolation device and/or parallel to a central axis which passes through the high-frequency filter and all the resonator chambers.
It is also advantageous in particular if the first signal line terminal, which engages in the indentation or in the continuous recess in the dielectric in the resonator chamber of the first resonator, is in contact with this dielectric or is arranged in this dielectric in a non-contact arrangement. The same is preferably also true of the second signal line terminal. In a non-contact arrangement, there is less coupling, but the assembly is simpler.
An example non-limiting method for adjusting the high-frequency filter comprises various process steps. In one process step, at the beginning all the coupling openings of the 1+Xth isolation device and/or the n−1−Xth isolation device are closed, where X is equal to 0 at the beginning. In another process step a reflection parameter is measured on the signal line terminal and/or on at least one, preferably all the signal line terminals. In addition, the resonant frequency and/or the coupling bandwidth and/or the input bandwidth is/are set at a desired level. With this method, the resonant frequency and/or the coupling bandwidth of m resonator chambers of a resonator chamber can be set at the desired level independently of additional resonator chambers in other resonator chambers.
Another advantage is achieved when one or both end faces of each of the n dielectrics is/are covered with a metal layer, wherein this metal layer is then one of the n−1 isolation devices and wherein at least one recess within the metal layer forms the at least one coupling opening. The use of suitably coated dielectrics allows a further reduction in the size of the high-frequency filter.
The housing preferably comprises a housing bottom and a housing cover at a distance from the housing bottom. Between the housing bottom and the housing cover:    a) a peripheral housing wall is arranged; or    b) at least one insert and one peripheral housing wall are arranged, the insert being enclosed by the peripheral housing wall, which also forms the outside wall of the high-frequency filter; or    c) at least one insert is arranged, forming a housing wall.
For the case when only one, preferably n inserts are used, the filter may have a very compact design. Then the n−1 isolation devices may be situated between the inserts. The lateral peripheral surfaces of the inserts as well as the lateral peripheral surface of the n−1 isolation devices form the peripheral wall of the housing in the embodiment variant c). In the embodiment variant b), in which the at least one insert is surrounded by a peripheral housing wall, the high-frequency filter has a very stable design.
Another advantage of the example non-limiting high-frequency filter is also when the diameter of at least one, preferably all the resonator chambers, is/are defined and/or predetermined by at least one insert, in particular by an annular insert, which leans against the housing wall. Therefore, the resonant frequency can be adjusted. The leaning of the insert on housing wall, in particular in a form-fitting manner, also ensures that the insert cannot be displaced out of its position over time.
Another advantage of the example non-limiting high-frequency filter is obtained when the inserts of at least two n resonator chambers that do not follow one another directly, i.e., are not adjacent to one another, have an opening, wherein the at least two openings are connected to one another by a duct, which runs at least partially inside the housing wall, for example. An electric conductor runs in this duct, wherein the electric conductor couples the two resonator chambers of the different resonator chambers capacitively and/or inductively to one another. In this way, despite the compact design of the high-frequency filter, it is possible to achieve a cross-coupling between two resonators not directly adjacent to one another.
The n dielectrics may be disk-shaped inside the high-frequency filter and/or all or some of the n dielectrics may be completely different or partially different in their dimensions. It is also possible for all or at least one of the n dielectrics to fill up some or all of the volume of its/their respective resonator chamber and thus the m resonator chambers. Due to the geometric design and the arrangement of the dielectrics, the behavior of each resonator with respect to its resonator frequency and its coupling bandwidth can be adjusted accordingly.
The coupling between the individual resonators is increased if the dielectric in the first resonator is in contact with the first isolation device and the dielectric in the nth resonator is in contact with the n−1th isolation device wherein the other dielectrics in the remaining n−2 resonators are in contact with both isolation devices adjacent to the respective resonator chamber. It is particularly advantageous if the dielectric in the nth resonator is in contact with the housing bottom when the dielectric in the first resonator is also in contact with the housing cover. The phrase “to be in contact with” is understood to mean that two structures at least touch one another. The dielectrics of the n resonator chambers are preferably fixedly connected to the respective isolation device or the respective isolation devices, so that the coupling is improved.
Another advantage of the high-frequency filter is that the arrangement and/or size and/or cross-sectional shape of at least one coupling opening of one of the n−1 isolation devices differs completely or partially from the arrangement and/or size and/or cross-sectional shape of one of the other ones of the n−1 isolation devices. It is also possible for the number of coupling openings in the n−1 isolation devices to be completely or partially different from one another. The coupling between the individual resonators can therefore be set at the desired level.
For further tuning of the high-frequency filter, it is also possible for the at least one, preferably all the resonator chambers of at least one, preferably all resonator chambers to have at least one additional opening toward the outside of the housing, wherein at least one tuning element can be inserted into the resonator chamber of at least one resonator chamber through this additional opening. The distance between the tuning element, which is inserted into the at least one resonator chamber of at least one resonator chamber through the at least one additional opening, and the corresponding dielectric can be altered to the corresponding respective dielectric inside the at least one resonator chamber in the at least one resonator chamber. A plurality of tuning elements may also be inserted into a resonator chamber, wherein one tuning element may consist entirely of a metal or a metallic coating, whereas the other tuning element consists of a dielectric material, for example. The tuning element that is made of a metallic material may be used for approximate tuning and the tuning element that is made of a dielectric material may be used for fine tuning of the resonant frequency and/or of the coupling bandwidth of the corresponding resonator.
The distance between the at least one spacer element and the respective dielectric within the resonator chamber can also be reduced to such an extent that it is in direct contact with the latter. The dielectric of each resonator chamber may also have at least one indentation, wherein the distance between the tuning element and the dielectric can be reduced to such an extent that the tuning element is inserted into the indentation in the respective dielectric and is thereby in contact with it. The tuning element is inserted into the resonator chamber at a right angle to the signal transmission direction in particular.
The method for adjusting the high-frequency filter is repeated accordingly for the other resonator chambers. After the resonant frequency and/or the coupling bandwidth of the first and/or last resonator chamber, i.e., the nth resonator chamber, has been set, then in an additional process step, at least one coupling opening of the 1+Xth isolation device and/or of the n−1−Xth isolation device is opened. In addition, the value of the counter variable X is incremented by 1. Next, the previous process steps are carried out again. A reflection factor is measured on the first signal line terminal and/or a reflection factor on the second signal line terminal, is measured. Following that, the coupling openings to the next resonators in the next resonator chamber are opened and the value of the counter variable is incremented again. The adjustment of the high-frequency filter begins with the resonators, in which the signal line terminals engage, i.e., with the outermost resonators, and it ends with the resonator or the resonators at the center of the high-frequency filter.
For the case when the high-frequency filter has an odd number of resonator chambers, the resonator at the center of the high-frequency filter must be used once for measurement of the reflection factor on the first signal line terminal and another time for the measurement of the reflection factor on the second signal line terminal. The coupling openings of the two isolation devices surrounding the resonator at the center of the high-frequency filter must be closed with respect to the other signal line terminal, depending on the measurement of the respective reflection factor.
Following that, or when all the coupling openings have been opened in the case of an even number of resonators, the forward transmission factor and/or the reverse transmission factor must also be measured on the first signal line terminal and/or on the second signal line terminal, in addition to measuring the reflection factors.
The resonant frequencies and/or the coupling bandwidths can be changed for each resonator by changing the diameter of the resonator chamber, which is possible, for example, by replacing the at least one insert with one other insert having different dimensions, for example. The arrangement and/or number and/or size and/or cross-sectional shape of the at least one coupling opening can also be altered by rotation and/or replacement of the at least one isolation device. Tightening or loosening at least one tuning element and at least one resonator chamber of a resonator chamber also makes it possible to alter the resonant frequency and/or the coupling bandwidth. Finally, the dielectric in the resonator chamber can also be replaced by another dielectric having different dimensions.